1. Field of the Invention
This invention relates to a trichromatic beam splitting arrangement adapted to direct light energy incident thereon into three mutually orthogonal ray paths.
2. Description of the Prior Art
In video transmission systems, and particularly in portable color television transmitting equipment, each video camera has a beam splitter arrangement disposed therein which is adapted to trifurcate light incident thereon into three ray paths.
Typically, the incident light energy impinges upon a lens element disposed perpendicularly to the axis of the incident beam. The light is focused by the lens and is passed through a bifurcating beam splitter disposed behind the lens. The bifurcating beam splitter splits the focused light energy into a first and a second ray path, the first ray path being directed toward the first of a plurality of vidicon tubes disposed in a bank of tubes. The axis of each tube in the bank is usually disposed perpendicularly to the axis of the incident light beam and parallel to each other.
Disposed directly behind the first beam splitter is a reflecting mirror operative to direct light in the second ray path toward a second beam splitter element. The second beam splitter is operative to bifurcate the light incident thereon into a first and a second ray path, one of the ray paths being directed toward a second vidicon tube while the second ray path from the second beam splitter is reflected by a second mirror and directed toward the third vidicon tube.
It is apparent that the vidicon tubes are each disposed a different focal length from the lens. Accordingly, it is necessary to provide some compensating lensing arrangement in the first and second ray paths from the second beam splitter in order to provide focused images to each of the vidicon tubes. In some arrangements the compensating lenses are embodied in a combined lens-filter arrangement. In the prior art portable television cameras require sophisticated compensating lensing arrangements as well as precision housings so that each of the vidicon tubes may be disposed at precisely the correct focal length from the lens.
It would be advantageous to provide an optical arrangement whereby light incident on a lens may be presented to three visual image planes each substantially the same focal length from the lens. Such an arrangement would appear to eliminate the need for complementary lensing arrangements and also simplify the mechanical mounting requirements of the housing.